Wave Equation Parameters from Driven‐Rod Test

Abstract

A method involving the use of driven‐rod test in conjunction with the measurement of high‐strain test (HST) data is introduced as an in‐situ testing technique for the determination of Smith model parameters, including the static soil resistance to pile driving and its distribution, the soil quake, and the Smith damping factor. A total of nine pile driving sites were visited to gather HST data for both prototype pile driving and dynamic small‐rod probing. Subsequently, a wave equation‐based computer program CAPWAP was used to derive the Smith model parameters following the CAPWAP signal match procedure. The model parameters deduced from HST data of the 30.5 cm outside diameter (OD) pipe piles and from the 2.8 cm OD driven rods exhibit significant differences. The observed differences are attributed to the differences in the shaft sizes, the rate of penetration (both velocity and acceleration), and possibly boundary conditions. An empirical extrapolation law based on the correlation studies is proposed for transferring the driven‐rod deduced Smith model parameters to the prototype pile driving conditions. To shed further insight on the observed differences of model parameters, examinations by means of cavity expansion theories are forwarded. The first‐order estimate of the effects of the size and rate of a penetrating shaft conforms with those derived from field HST data and the CAPWAP analysis. The proposed in‐situ testing techniques offers a viable method for the determination of Smith model parameters in an initial geotechnical site investigation, and can improve the reliability of wave equation‐predicted bearing graph for pile installation control.